The Andean civilizations were complex societies of many cultures and peoples mainly developed in the river valleys of the coastal deserts of PERU. They stretched from the Andes of southern Colombia southward down the Andes to CHILE and northwest Argentina . Archaeologists believe that Andean civilization first developed on the narrow coastal plain of the Pacific ocean. The CARAL OR NORTE of Peru is the oldest known civilization in the Americas, dating back to 3200 BCE.